The present invention relates to an apparatus for applying a foam-forming flowable reaction mixture to a substrate. The apparatus comprises an applicator tube which is connected to a mixer. The tube is provided with outlet openings and extends transversely over the substrate.
Apparatus of this type are used during the continuous production of laminated foam products and during the continuous production of polyurethane block foam on installations of this type. A continuous surface (e.g., a conveyor) with a surface layer placed on it, usually a sheet of paper, is passed beneath the applicator tube. The apparatus is also used during the discontinuous production of foam panels in a box and during the discontinuous production of block foam in a chest. The substrate rests in the form of an oblong box or an oblong chest while the applicator tube is passed over it. It goes without saying that the box or the chest can also be lined with a sheet.
The use of such an applicator tube is limited to small working widths because such an undesirable flow profile is formed with longer tubes that the substantially non-flow interface region on the internal wall increases in thickness towards the ends of the applicator tube. Due to the increased residence time in this region, the reaction mixture reacts fully before leaving the applicator tube, and cakes on and clogs up the applicator tube in the course of time. This leads to a rise in pressure in the applicator tube and the formation of larger cells which have a negative effect on the thermal conductivity of the finished polyurethane foam. During production of foam webs, i.e. polyurethane foam webs, it has proven advantageous, for this reason, and due to the requirement for a film of reaction mixture which as far as possible, is uniformly thick over the working width, to apply the foam mixture via a mixer head which oscillates over the working width. The applicator tube is oriented in the delivery direction of the product to be produced. The zig-zag application must be distributed and spread equally on the substrate. The outlay for the oscillation of the mixer head and optionally the spreading out of the layer applied is considerable. For working widths exceeding one meter it becomes more difficult to produce uniformly thick film with rapidly reacting chemical systems and/or high production rates.
With block foam installations in which the applied layer of reaction mixture is a few centimeters, the distribution of the reaction mixture is not quite so problematic. An applicator tube which branches into several outlets has been used for larger working widths. Nevertheless, there is a risk that the various streams will create transition zones in the cross-section of the foam block produced in those central regions in which they converge. The transition zones have a pore size or density which differs from that in other regions.
The object of the present invention is therefore to improve the apparatus of the type mentioned in such a way that it cannot clog as the result of reacting reaction mixture during operation and so that a uniform application is ensured for achieving a perfect end product, even with greater working widths.